1. Field of the Invention
This invention relates to a catalyst component or catalyst system that is useful for polymerizing or copolymerizing alpha-olefins and more particularly concerns a magnesium-containing supported titanium- and vanadium-containing alpha-olefin polymerization or copolymerization catalyst component or catalyst that is useful for producing a homopolymer or copolymer of an alpha-olefin having a broadened molecular weight distribution.
2. Discussion of the Prior Art
Although many polymerization and copolymerization processes and catalyst systems have been described, it is advantageous to tailor a process and catalyst system to obtain a specific set of properties of a resulting polymer or copolymer product. For example, in certain applications a product with a broader molecular weight distribution is desirable. Such a product has a lower melt viscosity at high shear rates than a product with a narrower molecular weight distribution. Many polymer or copolymer fabrication processes which operate with high shear rates, such as injection molding, oriented film, and thermobonded fibers, would benefit with a lower viscosity product by improving throughput rates and reducing energy costs. Also important is maintaining high activity and low atactic levels such as measured by hexane soluble and extractable materials formed during polymerization or copolymerization. Thus, it is highly desirable to develop a catalyst or catalyst component that is useful for producing a homopolymer or copolymer of an alpha-olefin having a broadened molecular weight distribution.
Magnesium-containing supported titanium halide-based alpha-olefin polymerization or copolymerization catalyst components or catalyst systems containing such components are now well known in the art. Typically, these catalyst components and catalyst systems are recognized for their performance based on activity and stereospecificity. However, commercial olefin polymerization or copolymerization, requires additional catalyst attributes for economical large-scale operation. Whatever the cause, production of small polymer particles and polymer of broad particle size distribution are disadvantageous for several reasons. From the standpoint of polymerization process efficiency, high levels of small polymer particles can cause problems because the particles tend to accumulate in, and plug, process lines and filters. From the standpoint of handling and processing of polyolefins, small polymer particles and broad particle size distribution can be disadvantageous because polymer bulk density often is lower than desired and an extrusion and/or pelletization step often is required prior to processing. In fact, numerous individual processes or process steps have been disclosed which have as their purpose the provision of improved supported, magnesium-containing, titanium-containing, electron donor-containing olefin polymerization or copolymerization catalysts. For example, Arzoumanidis et al., U.S. Pat. No. 4,866,022 discloses a method for forming a particularly advantageous alpha-olefin polymerization or copolymerization catalyst or catalyst component that involves a specific sequence of specific individual process steps such that the resulting catalyst or catalyst component has exceptionally high activity and stereospecificity combined with very good morphology. A solid hydrocarbon-insoluble, alpha-olefin polymerization or copolymerization catalyst or catalyst component with superior activity, stereospecificity and morphology characteristics is disclosed as comprising the product formed by 1) forming a solution of a magnesium-containing species from a magnesium hydrocarbyl carbonate or magnesium carboxylate; 2) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane; 3) reprecipitating such solid particles from a mixture containing a cyclic ether; and 4) treating the reprecipitated particles with a transition metal compound and an electron donor.
Arzoumanidis et al., U.S. Pat. No. 4,540,679 disclose a process for the preparation of a magnesium hydrocarbyl carbonate by reacting a suspension of a magnesium alcoholate in an alcohol with carbon dioxide and reacting the magnesium hydrocarbyl carbonate with a transition metal component.
Arzoumanidis et al., U.S. Pat. No. 4,612,299 disclose a process for the preparation of a magnesium carboxylate by reacting a solution of a hydrocarbyl magnesium compound with carbon dioxide to precipitate a magnesium carboxylate and reacting the magnesium carboxylate with a transition metal component.
While each of the processes of the aforesaid U.S. Pat. Nos. 4,866,022; 4,540,679; and 4,612,299 affords alpha-olefin polymerization or copolymerization catalysts or catalyst components which afford polymer or copolymer products which have desirable characteristics, it is highly desirable to develop additional alpha-olefin polymerization or copolymerization catalysts or catalyst components that afford polymers or copolymers which have a broadened molecular weight distribution.
In this regard, J. C. W. Chien, X. Zhou and S. Lin, Macromolecules, 22, 4134 (1989), and X. Zhou, S. Lin and J. C. W. Chien, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 28, 2609-2632 (1990), report that the substitution of vanadium for titanium in supported catalysts for the polymerization of propylene to form polypropylene results in the formation of polypropylene with a substantially higher molecular weight. However, none of the aforesaid U.S. Pat. Nos. 4,540,679; 4,612,299 or 4,866,022 disclose the presence of a vanadium component in the solid catalyst components disclosed therein.
Japanese Patent Application No. 60130605, published Jul. 12, 1985, does disclose a method in which both vanadium and titanium are incorporated into a solid polymerization catalyst component during solidification of the solid catalyst component. In particular, the solid catalyst component is disclosed as being formed by dissolving a magnesium halide in alcohol and then adding to the solution a mixture of titanium tetrahalide and a vanadium compound, to thereby precipitate the solid catalyst component.
Sato et al., U.S. Pat. No. 4,103,078 and Takamura et al., U.S. Pat. No. 4,190,555 disclose methods for making such supported polymerization catalysts in which both titanium and vanadium are present in the supported catalyst and in which methods the titanium and vanadium components are incorporated into the solid catalyst component while the solid catalyst component is being formed by precipitation from a solution. For example, Sato et al., U.S. Pat. No. 4,103,078 disclose a method in which a solid metal oxide selected from a group including magnesium oxide and vanadium pentoxide and a solid trivalent metal halide from the group consisting of aluminum chloride, aluminum bromide and ferric chloride, are mill-mixed together and then reacting the resultant mixture with a transition metal compound selected from the group consisting of titanium tetrachloride, vanadium tetrachloride and vanadium oxytrichloride in the presence of an aromatic compound, to form a solid product. Takamura et al., U.S. Pat. No. 4,190,555 disclose a method for reacting (1) a titanium compound, (2) a metal of Group II or III of the Periodic Table, and (3) a halide of a metal or Group II or III, in the presence of aromatic compounds, to obtain a reaction product which is treated first with an oxygen-containing organic compound and next with a tetrachloride of titanium, vanadium or both, to form a solid activated catalyst component.
In addition, there are numerous disclosures of methods for producing solid supported polymerization catalyst components in which titanium and vanadium components are introduced into the solid support after the solid support has been produced. Such disclosures include Japanese Patent Application No. 60192709, published Oct. 1, 1985; Japanese Patent Application No. 60081210, published May 9, 1985; Japanese Patent Application No. 59221311, published Dec. 12, 1984; Serra et al., U.S. Pat. No. 3,257,369; Kashiwa, U.S. Pat. No. 3,647,772; Matsura et al., U.S. Pat. No. 4,022,958; Kuroda et al., U.S. Pat. No. 4,061,857; Sano et al., U.S. Pat. No. 4,223,117; Sakurai et al., U.S. Pat. No. 4,330,646; Muja et al., U.S. Pat. No. 4,431,568; and Schmidt, U.S. Pat. No. 4,525,551.
In addition, polymer or copolymer morphology is often critical and typically depends upon catalyst morphology. Good polymer morphology generally involves uniformity of particle size and shape, resistance to attrition and an acceptably high bulk density. Minimization of very small particles (fines) typically is very important especially in gas-phase polymerizations or copolymerizations in order to avoid transfer or recycle line pluggage. Therefore, it is highly desirable to develop alpha-olefin polymerization and copolymerization catalysts and catalyst components that have good morphology, and in particular, a narrow particle size distribution. Another property which is important commercially is the maintenance of an acceptably high bulk density.